Method of making ferric chloride with reduced amounts of hydrochloric acid for water treatment

ABSTRACT

The present invention involves a system and method of making ferric chloride with reduced amounts of hydrochloric acid for water treatment. The method comprises preparing a reactant batch comprising ferric oxide and hydrochloric acid at a predetermined molar ratio. The method further includes mixing the reactant batch with an impeller rotating between about 60 and 150 revolutions per minute. The method further includes maintaining the reactant batch at a temperature between about 70° Fahrenheit and 180° Fahrenheit. The method forms a reaction product including ferric chloride and a reduced amount of hydrochloric acid.

BACKGROUND OF THE INVENTION

The present invention relates to systems and methods of making ferricchloride with reduced amounts of hydrochloric acid for water treatment.

Processes of making ferric chloride are known. Ferric chloride has beenused in the various industries for many years. For instance, ferricchloride is a component used in water treatment processes. Althoughcurrent processes of making ferric chloride are adequate, such processescan be improved. For example, many current systems and processesundesirably require chlorine to be reacted with an aqueous solution offerrous chloride in a recycled aqueous solution of ferric chloride. Anumber of steps follow which include decompressing and vaporizing areaction product, recycling the reaction product, and recovering thereaction product. Such process requires numerous process units to makeferric chloride which, in turn, requires costly transportation to atypically remote location.

Many processes of making ferric chloride produce a product havingrelatively large amounts of hydrochloric acid. Relatively large amountsof hydrochloric acid are undesirable in water treatment processes.Moreover, in many processes of making ferric chloride, numerous stepsare required to reduce the amount of hydrochloric acid from the product.Additionally, in such processes, a relatively large number of processunits are required to reduce the hydrochloric acid concentration.Furthermore, in turn, the equipment for these processes require asignificant measure of space, more than typically available near watertreatment plants, thus requiring costly means for transporting ferricchloride to subsequent water treatment plants via rail car or trailers.

Therefore, it is desirable to improve the process of making ferricchloride by reducing the amount of hydrochloric acid concentration fromthe product to be used in water treatment processes. Moreover, it isfurther desirable to reduce the number of steps and process unitsrequired in making ferric chloride. Furthermore, it is also desirable toreduce the amount of area required to make ferric chloride, therebyeliminating or reducing transportation costs.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, a method of making ferric chloride comprisespreparing a reactant batch comprising ferric oxide and hydrochloric acidat a predetermined molar ratio. The method further includes mixing thereactant batch with an impeller rotating between about 60 and 150revolutions per minute, and maintaining the reactant batch at atemperature between about 70° Fahrenheit and 180° Fahrenheit. The methodforms a reaction product including ferric chloride and a reduced amountof hydrochloric acid.

In another embodiment, a system for making ferric chloride comprises abatch reactor for receiving a reactant batch comprising ferric oxide andhydrochloric acid in aqueous solution at a predetermined molar ratio.The batch reactor has baffles disposed on its inner side walls, and amixer having a rotating shaft and an impeller disposed adjacent thebottom of the reactor. The batch reactor is configured to mix thereactant batch at an agitation speed between about 60 and 150revolutions per minute and to form a reaction product comprising ferricchloride and a reduced amount of hydrochloric acid. The system furtherincludes a scrubber in fluid communication with the batch reactor toreceive hydrochloric acid vapors vented from the batch reactor, and afilter in fluid communication with the batch reactor for filtering thereaction product.

Further objects, features and advantages of the invention will becomeapparent from consideration of the following description and theappended claims when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a depicts a process flow diagram of a first portion of one systemfor making ferric chloride in accordance with one embodiment of thepresent invention;

FIG. 1 b depicts a process flow diagram of a second portion of thesystem in FIG. 1 a; and

FIG. 2 depicts a flow chart of one method of making ferric chloride inaccordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 a and 1 b illustrate process flow diagrams of a system 10 formaking ferric chloride with reduced amounts of hydrochloric acid forwater treatment. As shown, the system 10 includes a relatively reducednumber of process units to make ferric chloride, allowing the system tobe transportable and occupy a relatively small area, thereby reducingtransportation costs and transit time of the ferric chloride to watertreatment units. System 10 generally includes a batch reactor 12 forreceiving a reactant batch of ferric oxide and hydrochloric acid inaqueous solution. As shown in FIG. 1 a, system 10 includes a pump 26 forrecycling the reactant batch components, heating the reactant batch, anddrawing reaction product from the batch reactor 12 to a filter unit 30.System 10 further includes heat exchanger system 32 across which thereactant batch may be pumped for heat transfer to the reactant batch.System 10 may also include a vent 34 to a scrubber system 33 for ventinghydrochloric acid vapors from the batch reactor. As shown, the scrubber33 receives the hydrochloric acid vapors, and exhaust gas is blown to astack of separation units for further processing of the exhaust gas.

In accordance with one embodiment of the present invention, system 10includes a batch reactor or “ferric reactor” 12 for receiving a reactantbatch of ferric oxide (Fe₂O₃) and hydrochloric acid (HCl) at apredetermined molar ratio. Preferably, the molar ratio of ferric oxideto hydrochloric acid in the reactant batch is 3:6. The hydrochloric acid(HCl) and ferric oxide (Fe₂O₃) react to form a reaction productincluding ferric chloride (FeCl₃), water (H₂O), unreacted hydrochloricacid, and residuals. A quantitative relationship of ferric oxide andhydrochloric acid to make ferric chloride may be represented in achemical reaction as follows:1Fe₂O₃+6HCl→2FeCl₃+3H₂O.

In this embodiment, batch reactor 12 has inner side walls 13 and abottom 14 integral with inner side walls 13. The inner side walls 13 andbottom 14 may have a protective lining (discussed below) to receive thereactant batch. In this embodiment, the batch reactor 12 is configuredto receive and mix a reactant batch comprised of ferric oxide andhydrochloric acid in aqueous solution. The batch reactor 12 isconfigured to mix the reactant batch at an agitation speed between about60 and 150 revolutions per minute (rpm) and to form a reaction productincluding ferric chloride, water, hydrochloric acid, unreacted ferricoxide, and residuals.

In particular, the batch reactor 12 is configured to form a reactionproduct of ferric chloride having reduced amounts of hydrochloric acid,e.g., between about 0.1 and 3 weight percent hydrochloric acid of thereaction product. As described in greater detail below, the batchreactor is configured to mix the reaction batch for about at least 1hour. Batch reactor 12 further includes a plurality of baffles 16disposed about inner side walls 13 to enhance mixing.

In this embodiment, the batch reactor 12 is designed to receive and holda reactant batch comprising ferric oxide and hydrochloric acid inaqueous solution. For example, the batch reactor may be a reactormanufactured by Belding™ Tank Technologies, model CFV-10 being a 5915filament wound reinforced fiberglass lined tank having a dome top and aflat bottom. The capacity of the batch reactor is preferably at leastabout 4,000 gallons. In this embodiment, the capacity of the batchreactor is about 5,900 gallons. The batch reactor has dimensions of 120inches diameter×120 inches straight side×140 inches overall height.

The fiberglass liner of the batch reactor may be comprised of polymericresins including premium grade Derakane 441™ vinyl ester resinsthroughout and may include an internal veil of double glass with 200 milcorrosion barrier. The batch reactor may have an external coat ofpremium grade protective coating with an ultraviolet inhibitor. In thisembodiment, the batch reactor is designed for 1.9 specific gravityproduct and for having a −8″ water column vacuum. The batch reactor mayhave reinforcement ribs on the flat bottom. The reactor may preferablyinclude four anti-swirl baffles, of a type such as known in the art,substantially evenly spaced out between each other on the inner sidewalls.

In this embodiment, batch reactor 12 further includes a mixer 15 havinga rotating shaft 17 and an impeller 18 connected to the shaft 17. Bladesof the impeller may be located adjacent the bottom 14 of the reactor 12.Impeller 18 enables mixing of reactants within the batch reactor 12 byway of a drive motor 19 connected to the rotating shaft 17. Motor 19 isconfigured to rotatably drive the shaft 17 thereby rotating the impeller18 within the batch reactor 12. In this embodiment, the motor 19 hasvariable speeds at which the impeller may be rotated. Batch reactor 12also includes a temperature indicator 20 such as known in the art formeasuring temperature of a reaction batch during normal operation.

In this embodiment, the mixer is a GA Braun™ mixer model 4BTO5-70 mixerassembly driven by a five horse power motor having a three phase, 60cycle, 1750 rpm, 230/460 volt motor geared for 70 rpm output. Theimpeller is a GA Braun™ A35 single-blade impeller unit with a stabilizermounted on a 2½ inch diameter×122 inch long shaft. The mixer is mountedon an eight inch, 150 pound ANSI flange with a low pressure stuffing box(15 psig). Wetted parts, e.g., blades of the impeller, are 304 stainlesssteel, rubber lined with high temperature core butyl.

As shown, the system 10 further includes a hydrochloric acid input line22 from a hydrochloric acid source. The hydrochloric acid source may beany suitable source, such as a holding tank for hydrochloric acid inaqueous solution. The system 10 further includes a ferric oxide inputline 24 from a ferric oxide source which may be any suitable sourceincluding a storage facility for ferric oxide in solid phase.

At ambient temperatures of about 65° Fahrenheit or greater, it has beendetermined that a minimum volume or mass of the reactant batch may beused so that the resulting exothermic reaction produces sufficient heatto maintain the reactant batch at a desired temperature range duringmixing. In this embodiment, the desired temperature of the reactantbatch is between about 70° and 180° Fahrenheit. Thus, at thosetemperatures and with mixing of between about 60 and 150 rpm, it hasbeen surprisingly found that no heat source or heat exchange system isrequired to form the reaction product.

However, it also has been found that when using reactant batch volumesbelow the minimum volume, the heat generated by the resulting exothermicreaction is insufficient to maintain the reactant batch at the desiredtemperature range during mixing. In this embodiment, it is preferredthat at least 4,000 gallons of reactant batch is used to maintain thereactant batch at the desired temperature range.

Preferably, hydrochloric acid in aqueous solution is introduced to thebatch reactor. Then, ferric oxide in solid form is added to thehydrochloric acid in aqueous solution, defining the reactant batch. Inthis embodiment, the hydrochloric acid is supplied from a supply tank(not shown) containing between about 32 and 37 weight percenthydrochloric acid and between about 68 and 63 weight percent water. Asmentioned, the ferric oxide supply is preferably in solid (powder) formas it is introduced in the batch reactor after the hydrochloric acid isreceived in the batch reactor. In this embodiment, the ferric oxidesupply includes about 99 weight percent of ferric oxide in powder form.

In this embodiment, the hydrochloric acid concentration in the reactantbatch is between about 20 weight percent and 30 weight percent of thereactant batch in aqueous solution, and preferably about 23 weightpercent and 27 weight percent of the reactant batch in aqueous solution.The hydrochloric acid concentration is more preferably about 25 weightpercent of the reactant batch in aqueous solution.

In this embodiment, it is preferred that the ferric oxide used in thereactant batch be added in solid phase, e.g., powder form. Theconcentration of the ferric oxide is between about 10 weight percent and30 weight percent of the reactant batch, and preferably between about 15weight percent and 25 weight percent of the reactant batch. The ferricoxide concentration in the reactant batch is more preferably about 20weight percent.

At temperatures less than about 65° Fahrenheit, a heat exchange systemis used to provide heat to maintain the reactant batch at the desiredtemperature range. It is to be understood that a heat exchange system ispreferably used when the batch reaction time is less than three hours orwhen the process is at an ambient temperature of less than 65°Fahrenheit.

As shown, a recycle pump 26 is in fluid communication with the batchreactor 12 to selectively draw product or batch components from thebatch reactor. Recycle pump 26 may be used for pumping components of thereactant batch through the heat exchanger 32, drawing product from thebatch reactor, or recycling components of the reactant batch within thebatch reactor. In this embodiment, the recycle pump is a fiberglass pump3″ (inlet)×1.5″ (outlet) with a 15 horse power variable speed drive.

A filter unit 30 may be in fluid communication with the recycle pump forfiltering unreacted ferric oxide and residuals, such as dirt and sand,from the reaction product. As shown, the filter unit 30 may have anoutlet 31 which allows filtered reaction product to be conveyed totransportation vehicles or storage facilities such as trailers,railcars, or storage tanks. In this embodiment, the reaction productgenerally includes ferric chloride and the reduced amount ofhydrochloric acid. In this embodiment, the filter unit 30 has filterswhich may be cartridge type filters made of polypropylene retained in ahousing made of rubber lined steel.

As shown, system 10 further includes a heat exchanger/boiler system 32for heating components of the reactant batch or the reaction product tomaintain a temperature between about 70° Fahrenheit and 180° Fahrenheit.The heat exchanger system 32 may be configured to heat the reactionproduct to be recycled within the batch reactor, the reactant batch, orcomponents of the reactant batch.

The heat exchanger/boiler system may include any suitable heat exchangerand boiler known in the art. In this embodiment, the heat exchanger is ashell and tube heat exchanger wherein the shell is made of carbon steeland the tubes are made of tantalum. In this embodiment, the heatexchanger requires a minimum surface area of about 60 ft². In thisembodiment, the heat exchanger is rated for up to about 100 psig steampressure. The heat exchange system should operate at a minimum of about3 million Btu per hour wherein the boiler steam is between about 10 psigand 90 psig.

As shown, a scrubber unit 33 may be in fluid communication with batchreactor 12 by way of a vent line 34 to receive hydrochloric acid vaporsfrom the batch reactor. In this embodiment, the vent line 34 mayconverge with vent lines from other sources such as trucks and storagetanks as shown. As such, a blower 36, located downstream of the scrubberunit 33, may be used to damper the hydrochloric acid to the atmosphere.

The scrubber unit 33 for the hydrochloric acid vent 34 is configured tobe able to pull a vacuum of −3 inches of water column and treat 1,000cubic feet per minute (cfm) of air flow. In this embodiment, thescrubber unit is made of fiberglass and the vent line is made of anysuitable material, e.g., fiberglass or chlorinated polyvinyl chloride(CPVC).

The system 10 forms a reaction product including a ferric chloridesolution having a reduced amount of hydrochloric acid. In thisembodiment, the ferric chloride is between about 20 and 50 weightpercent, and preferably 28 and 45 weight percent ferric chloride. Thereaction product further includes between about 50 and 80 weight percentwater, and preferably 55 and 72 weight percent water. The reactionproduct further includes between about 0.1 and 3 weight percenthydrochloric acid and preferably about 1 weight percent hydrochloricacid. Preferably, the ferric chloride is about 43 weight percent, thewater is about 56 weight percent, and the hydrochloric acid is about 1weight percent of the reaction product.

FIG. 2 is a flow chart depicting one method 110 of making ferricchloride with reduced amounts of hydrochloric acid. As shown, method 110comprises a step 112 of preparing a reactant batch comprising ferricoxide and hydrochloric acid at a predetermined molar ratio. Preparingthe reactant batch may include introducing hydrochloric acid in aqueoussolution and then introducing ferric oxide in solid phase, e.g., ferricoxide powder. The predetermined molar ratio of ferric oxide andhydrochloric acid is at least about 1:6, preferably 3:6. In thisembodiment, the ferric oxide is in solid phase (powder) and thehydrochloric acid is in aqueous solution.

The components of the reactant batch may be preheated by way of the heatexchange system discussed above and shown in FIG. 1. This may beaccomplished by recycling the component(s) with the recycle pump acrossthe heat exchanger for preheating. In this embodiment, the hydrochloricacid in aqueous solution may be preheated when conditions of the batchreactor have a temperature of equal to or less than 60° Fahrenheit.Optionally, a volume of reactant product may be retained in the batchreactor as the hydrochloric acid and the ferric oxide are introducedinto the batch reactor to minimize the concentration of hydrochloricacid in the batch reactor.

The method further includes a step 114 of mixing the reactant batch witha mixer having an impeller rotating between about 60 and 150 revolutionsper minute. In this embodiment, the impeller has a pumping capacity ofabout 19,000 gallons per minute. During mixing, the reactant batch ismixed with the impeller at turbulent flow. The impeller has a powernumber of about 6.7 at 1.5 specific gravity and a Reynolds number of8,150 at 200 cps. Preferably, the impeller rotates at about 70revolutions per minute (rpm). In this embodiment, mixing is performedfor about 1 to 3 hours. During mixing, the hydrochloric acid is sampledand tested by titration about every hour in this embodiment. When theweight percent of hydrochloric acid is determined to be about 3 percentor below, mixing may be stopped.

In this embodiment, the method 110 further includes a step 116 ofmaintaining the reactant batch at a desired temperature between about70° Fahrenheit and 180° Fahrenheit. Preferably, the reactant batch ismaintained at a temperature between about 165° Fahrenheit and 180°Fahrenheit. This may be accomplished with the heat exchange systemmentioned above or without the heat exchange system so long as thereactant batch is at a minimum volume, e.g., 4000 gallons, andsufficient mixing is provided, e.g., 60 rpm to 150 rpm.

Thus, the reactant batch may be at a predetermined mass or volume togenerate heat from the resulting exothermic reaction to sufficientlymaintain the reactant batch at the desired temperature, during mixing,without use of a heat exchange system. In one embodiment, the reactantbatch is at a minimum volume of at least 4,000 gallons, and preferablyabout 5900 gallons, to sufficiently maintain the desired temperature ofabout 70° Fahrenheit and 180° Fahrenheit during mixing.

At ambient temperatures of less than 65° Fahrenheit, a heat source isused to heat the reactant batch. This may be accomplished by way of theheat exchange system mentioned above. In this embodiment, the recyclepump draws the reactant batch across the heat exchanger for heattransfer to maintain the reactant batch between about 70° and 180°Fahrenheit. As a result, the reaction product is formed including aferric chloride solution having a reduced amount of hydrochloric acid.

Method 110 may further include venting hydrochloric acid vapors from thebatch reactor when mixing the reactant batch at the desired temperature.As discussed above, the hydrochloric acid vapors may be vented to ascrubber unit for hydrochloric acid vapor processing. Method 110 furtherincludes drawing the reaction product from the batch reactor andfiltering the reaction product of unreacted ferric oxide and residualstherefrom. As discussed above, this may be accomplished with the recyclepump and the filter unit.

EXAMPLE

About 3077 gallons of 37 weight percent hydrochloric acid in aqueoussolution was added in a 5900 gallon batch reactor tank manufactured byBelding™ Tank Technologies, Model CFV-10. The mixer of the tank wasactivated to rotate at 70 rpm to mix the ferric oxide and hydrochloricacid in aqueous solution. Then, four 2000-pound bags of 99.5 weightpercent ferric oxide in powder form were added to the hydrochloric acidin aqueous solution in the batch reactor, defining the reactant batch.The recycle pump was activated to pump the reactant batch across theheat exchange system to heat the reaction batch between about 70 and180° Fahrenheit. After about 1 hour of mixing and heating, the reactantbatch was at a temperature of about 165° Fahrenheit. Mixing and heatingcontinued for a total of 3 hours. After about 3 hours from adding thelast bag of ferric oxide to the reactant batch a reaction product wasformed.

The reaction product was analyzed and had about 41 weight percent ferricchloride, 58 weight percent water, and 1 weight percent hydrochloricacid of the reaction product.

It should be appreciated that the example, method, and system of thepresent invention are capable of being incorporated in the form of avariety of embodiments, only a few of which have been illustrated anddescribed above. The invention may be embodied in other forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrated andnot restrictive, and the scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A method of making ferric chloride with low amount of hydrochloricacid for water treatment, the method comprising: preparing a reactantbatch comprising ferric oxide and hydrochloric acid added at apredetermined molar ratio; mixing the reactant batch with an impellerrotating between about 60 and 150 revolutions per minute; maintainingthe reactant batch at a temperature between about 70° and 180°Fahrenheit; whereby a reaction product including ferric chloride with alow amount of hydrochloric acid is formed.
 2. The method of claim 1wherein the predetermined molar ratio of ferric oxide to hydrochloricacid is at least about 1:6.
 3. The method of claim 1 wherein thepredetermined molar ratio of ferric oxide to hydrochloric acid is atleast about 3:6.
 4. The method of claim 1 wherein preparing the reactantbatch includes: introducing hydrochloric acid in the form of aqueoussolution; and introducing ferric oxide in the form of a solid phase. 5.The method of claim 1 wherein the ferric oxide added is between about 10weight percent to 30 weight percent and the hydrochloric acid is betweenabout 20 weight percent to 30 weight percent of the reactant batch inaqueous solution.
 6. The method of claim 5 wherein the ferric oxideadded is about 20 weight percent and the hydrochloric acid is about 27weight percent of the reactant batch in aqueous solution.
 7. The methodof claim 1 wherein the impeller is a single impeller having a pumpingcapacity of about 19,000 gallons per minute.
 8. The method of claim 1wherein mixing the reactant batch with the impeller is at turbulentflow.
 9. The method of claim 1 wherein the impeller has a power numberof about 6.7 at 1.5 specific gravity and a Reynolds Number of 8,150 at200 cps.
 10. The method of claim 1 wherein the impeller rotates at about70 revolutions per minute.
 11. The method of claim 1 wherein thereactant batch is at a volume of at least 4,000 gallons to substantiallymaintain a temperature of about 70° Fahrenheit and 180° Fahrenheitduring mixing.
 12. The method of claim 1 wherein maintaining thereactant batch temperature includes using only the heat from theexothermic reaction of the reactant batch, when the reactant batchexceeds a predetermined volume and the ambient temperature is greaterthan 65° Fahrenheit.
 13. The method of claim 12 wherein thepredetermined volume of the reactant batch is at least about 4,000gallons.
 14. The method of claim 1 wherein the reactant batch ismaintained at a temperature between about 165° Fahrenheit and 180°Fahrenheit.
 15. The method of claim 1 wherein mixing is performed forabout 1 to 3 hours.
 16. The method of claim 1 wherein the reactionproduct includes between about 20 and 50 weight percent ferric chloride,between about 50 and 80 weight percent water, and between about 0.1 and3 weight percent hydrochloric acid.
 17. The method of claim 1 whereinthe reaction product includes about 43 weight percent ferric chloride,about 56 weight percent water, and about 1 weight percent hydrochloricacid.
 18. The method of claim 1 further comprising heating the reactantbatch to about 70° Fahrenheit to 180° Fahrenheit.
 19. The method ofclaim 1 further comprising filtering the reactant batch of unreactedferric oxide and residuals from the reaction product.
 20. The method ofclaim 1 wherein the low amount of hydrochloric acid range between about0.1 weight percent and 3 weight percent.
 21. The method of claim 1wherein the low amount of hydrochloric acid is less than about 3 weightpercent.
 22. A method of making ferric chloride with low amount ofhydrochloric acid for water treatment, the method comprising:introducing ferric oxide into an aqueous solution of hydrochloric acidat a predetermined molar ratio to form a reactant batch; heating thereactant batch to a desired temperature between about 70° Fahrenheit and180° Fahrenheit; mixing the reactant batch with a mixer rotating betweenabout 70 and 100 revolutions per minute at the desired temperature; andventing hydrochloric acid vapors from the reactant batch; forming areaction product including ferric chloride, water, with a low amount ofhydrochloric acid; and filtering the reaction product of unreactedferric oxide and residuals therefrom.
 23. The method of claim 22 whereinthe predetermined molar ratio of ferric oxide and hydrochloric acid isat least about 1:6.
 24. The method of claim 22 wherein the predeterminedmolar ratio of ferric oxide is about 3:6.
 25. The method of claim 22wherein the ferric oxide is introduced in the form of a solid.
 26. Themethod of claim 22 wherein the ferric oxide is between about 20 weightpercent and 25 weight percent and the hydrochloric acid is between about24 weight percent and 27 weight percent of the reactant batch in aqueoussolution.
 27. The method of claim 26 wherein the ferric oxide is about20 weight percent and the hydrochloric acid is about 25 weight percentof the reactant batch in aqueous solution.
 28. The method of claim 22wherein heating the reactant batch includes generating heat from anexothermic reaction of the reactant batch having a predetermined volumeto maintain a temperature at the desired temperature of between about70° Fahrenheit and 180° Fahrenheit.
 29. The method of claim 22 whereinthe predetermined volume of the reactant batch is at least about 4,000gallons.
 30. The method of claim 22 wherein heating the reactant batchincludes maintaining the reactant batch at a temperature between about165° Fahrenheit and 180° Fahrenheit.
 31. The method of claim 22 whereinmixing is performed for about 1 to 3 hours.
 32. The method of claim 22wherein the ferric chloride is between about 20 and 50 weight percent,the water is between about 50 and 80 weight percent, and thehydrochloric acid is between about 0.1 and 3 weight percent of thereaction product.